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Re: curl_multi_remove_handle callbacks - debug mode?
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From: Felipe Gasper via curl-library <curl-library_at_cool.haxx.se>
Date: Thu, 13 May 2021 08:35:25 -0400
> On May 13, 2021, at 6:10 AM, Daniel Stenberg <daniel_at_haxx.se> wrote:
>
> On Wed, 12 May 2021, Felipe Gasper via curl-library wrote:
>
>> On a couple of occasions now I’ve chased down segfaults that it turned out were happening because a callback was freeing the multi.
>
>> Is there any kind of “debug mode” in libcurl available that would warn, assert, or otherwise complain if something like that happens? I _think_ I have a fix in place that will prevent the issue moving forward, but that’s what I thought last time I fixed this problem. :-P
>>
>> If there’s not such a mode available, would that be a reasonable feature to add?
>
> curl_multi_remove_handle doesn't "free the multi" though, so it sounds like you're mixing something here.
>
> curl_multi_cleanup() will already not accept getting called from within a callback:
>
> https://github.com/curl/curl/blob/dae382a1a1481a94b708c82d5aa9fa7253084160/lib/multi.c#L2555-L2557
>
> curl_multi_remove_handle also tries to detect and avoid getting called from within a callback:
>
> https://github.com/curl/curl/blob/dae382a1a1481a94b708c82d5aa9fa7253084160/lib/multi.c#L740-L741
>
> ... but since you write this, I assume something makes these conditional checks not be good enough. Can you figure out why? And if so, how would such an additional "debug check" you speak of work that isn't already checked for?
You know … I neglected to mention before that I’m constrained to use OS-provided curls … which in CentOS 7 means 7.29.
So yeah, this problem is already solved; our curl is just too old to have the fix.
Yet another justification, though, for why we should build our own curl. :)
Thank you!
-FG
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Received on 2021-05-13
Date: Thu, 13 May 2021 08:35:25 -0400
> On May 13, 2021, at 6:10 AM, Daniel Stenberg <daniel_at_haxx.se> wrote:
>
> On Wed, 12 May 2021, Felipe Gasper via curl-library wrote:
>
>> On a couple of occasions now I’ve chased down segfaults that it turned out were happening because a callback was freeing the multi.
>
>> Is there any kind of “debug mode” in libcurl available that would warn, assert, or otherwise complain if something like that happens? I _think_ I have a fix in place that will prevent the issue moving forward, but that’s what I thought last time I fixed this problem. :-P
>>
>> If there’s not such a mode available, would that be a reasonable feature to add?
>
> curl_multi_remove_handle doesn't "free the multi" though, so it sounds like you're mixing something here.
>
> curl_multi_cleanup() will already not accept getting called from within a callback:
>
> https://github.com/curl/curl/blob/dae382a1a1481a94b708c82d5aa9fa7253084160/lib/multi.c#L2555-L2557
>
> curl_multi_remove_handle also tries to detect and avoid getting called from within a callback:
>
> https://github.com/curl/curl/blob/dae382a1a1481a94b708c82d5aa9fa7253084160/lib/multi.c#L740-L741
>
> ... but since you write this, I assume something makes these conditional checks not be good enough. Can you figure out why? And if so, how would such an additional "debug check" you speak of work that isn't already checked for?
You know … I neglected to mention before that I’m constrained to use OS-provided curls … which in CentOS 7 means 7.29.
So yeah, this problem is already solved; our curl is just too old to have the fix.
Yet another justification, though, for why we should build our own curl. :)
Thank you!
-FG
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Received on 2021-05-13